U.S. patent number 4,048,139 [Application Number 05/549,040] was granted by the patent office on 1977-09-13 for rendering polybenzimidazole solid materials more resistant to darkening upon exposure to light.
This patent grant is currently assigned to Celanese Corporation. Invention is credited to Gordon W. Calundann, Edward J. Powers.
United States Patent |
4,048,139 |
Calundann , et al. |
September 13, 1977 |
Rendering polybenzimidazole solid materials more resistant to
darkening upon exposure to light
Abstract
A route is provided for the formation of a polybenzimidazole
solid material having an enhanced resistance to undergo the usual
color darkening upon exposure to light. A minor concentration of a
finely divided pigment found capable of stabilizing the background
color inherently manifest by the polybenzimidazole polymer is
dispersed in a solution of the polybenzimidazole, and the solvent
is removed to produce a polybenzimidazole solid having the pigment
substantially uniformly distributed therein. The pigment utilized
may be arsenic thioarsenate, copper phthalocyanine, anatase
titanium dioxide, or mixtures thereof. Fibers, films,
three-dimensional shaped articles, etc. may be formed from the
color stabilized polybenzimidazole.
Inventors: |
Calundann; Gordon W. (North
Plainfield, NJ), Powers; Edward J. (Gillette, NJ) |
Assignee: |
Celanese Corporation (New York,
NY)
|
Family
ID: |
24191416 |
Appl.
No.: |
05/549,040 |
Filed: |
February 11, 1975 |
Current U.S.
Class: |
524/88; 524/104;
524/173; 524/233; 524/234; 524/235; 524/408; 524/547; 524/548;
524/549; 524/612 |
Current CPC
Class: |
C08G
73/18 (20130101); C08K 5/0041 (20130101); C08K
5/0041 (20130101); C08L 79/04 (20130101); C08K
3/013 (20180101); C08K 3/013 (20180101); C08L
79/04 (20130101) |
Current International
Class: |
C08L
79/00 (20060101); C08G 73/00 (20060101); C08G
73/18 (20060101); C08L 79/04 (20060101); C08K
003/22 (); C08K 003/30 (); C08K 005/34 (); C08K
005/36 () |
Field of
Search: |
;260/45.7R,78.4R,32.6N,45.85R,45.75B,45.75C,45.75F,37N,45.8N,3.8DS
;264/205 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"Handbook of Adhesives", 1962, Skeist, pp. 223, 447..
|
Primary Examiner: Cockeram; H.S.
Claims
We claim:
1. An improved process for the formation of a polybenzimidazole
solid material having an enhanced resistance to undergo the usual
color darkening upon exposure to light comprising:
a. forming a solution of polybenzimidazole in a solvent selected
from the group consisting essentially of N,N-dimethyacetamide,
N,N-dimethylformamide, dimethylsulfoxide, and
N-methyl-2-pyrrolidone, with said solution having dispersed therein
a minor concentration of finely divided pigment selected from the
group consisting essentially of arsenic thioarsenate, copper
phthalocyanine, anatase titanium dioxide, and mixtures of the
foregoing, and
b. substantially removing said solvent from said polybenzimidazole
to form a polybenzimidazole solid material wherein said finely
divided pigment is substantially uniformly dispersed therein in a
concentration of about 0.1 to 8 percent by weight based upon the
weight of the polybenzimidazole.
2. An improved process in accordance with claim 1 for the formation
of a polybenzimidazole solid material having an enhanced resistance
to undergo color darkening upon exposure to light wherein said
polybenzimidazole consists essentially of recurring units of the
formula: ##STR4## wherein R is a tetravalent aromatic nucleus, with
the nitrogen atoms forming the benzimidazole rings paired upon
adjacent carbon atoms of said aromatic nucleus, and R' is selected
from the group consisting of (1) an aromatic ring, (2) an alkylene
group having from 4 to 8 carbon atoms, and (3) a heterocyclic ring
selected from the group consisting of (a) pyridine, (b) pyrazine,
(c) furan, (d) quinoline, (e) thiophene, and (f) pyran.
3. An improved process in accordance with claim 2 for the formation
of a polybenzimidazole solid material having an enhanced resistance
to undergo color darkening upon exposure to light wherein said
polybenzimidazole is
poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole.
4. An improved process in accordance with claim 1 for the formation
of a polybenzimidazole solid material having an enhanced resistance
to undergo color darkening upon exposure to light wherein said
finely divided pigment is provided in said solution in a
concentratio of about 0.1 to 8 percent by weight based upon the
weight of said dissolved polybenzimidazole.
5. An improved process in accordance with claim 1 for the formation
of a polybenzimidazole solid material having an enhanced resistance
to undergo color darkening upon exposure to light wherein said
finely divided pigment is arsenic thioarsenate.
6. An improved process in accordance with claim 1 for the formation
of a polybenzimidazole solid material having an enhanced resistance
to undergo color darkening upon exposure to light wherein said
finely divided pigment is copper phthalocyanine.
7. An improved process in accordance with claim 1 for the formation
of a polybenzimidazole solid material having an enhanced resistance
to undergo color darkening upon exposure to light wherein said
finely divided pigment is anatase titanium dioxide.
8. An improved process in accordance with claim 1 for the formation
of a polybenzimidazole solid material having an enhanced resistance
to undergo color darkening upon exposure to light wherein said
solvent is removed via dry spinning into an evaporative atmosphere
and said resulting polybenzimidazole solid material is a fibrous
material.
9. An improved process in accordance with claim 1 for the formation
of a polybenzimidazole solid material having an enhanced resistance
to undergo color darkening upon exposure to light wherein said
solvent is removed by evaporation from a thin layer of said
solution and the resulting polybenzimidazole solid material is a
film.
10. An improved process in accordance with claim 1 for the
formation of a polybenzimidazole solid material having an enhanced
resistance to undergo color darkening upon exposure to light
wherein said solvent is removed by contact with agitation with a
solvent-miscible non-solvent for said polybenzimidazole and said
resulting polybenzimidazole solid material is a particulate
solid.
11. An improved process in accordance with claim 1 for the
formation of a polybenzimidazole solid material having an enhanced
resistance to undergo color darkening upon exposure to light
wherein said finely divided pigment is substantially uniformly
dispersed therein in a concentration of about 0.2 to 3 percent by
weight based upon the weight of the polybenzimidazole.
12. An improved process for the formation of a
poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole fibrous material
having an enhanced resistance to undergo the usual darkening upon
exposure to light comprising:
a. forming a spinning solution comprising (1) a solvent selected
from the group consisting essentially of N,N-dimethylacetamide,
N,N-dimethylformamide, dimethylsulfoxide, and
N-methyl-2-pyrrolidone, (2) about 10 to 45 percent by weight based
upon the total weight of the solution of dissolved
poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole, and (3) about 0.1 to
8 percent by weight based upon the weight of said
poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole of dispersed finely
divided pigment selected from the group consisting essentially of
arsenic thioarsenate, copper phthalocyanine, anatase titanium
dioxide, and mixtures of the foregoing, and
b. extruding said solution through a shaped orifice into an
evaporative atmosphere to form a
poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole fibrous material
having said finely divided pigment substantially uniformly
distributed therein in a concentration of about 0.1 to 8 percent by
weight based upon the weight of said
poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole.
13. An improved process in accordance with claim 12 for the
formation of a poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole fibrous
material having an enhanced resistance to undergo color darkening
upon exposure to light wherein said solvent is
N,N-dimethylacetamide.
14. An improved process in accordance with claim 13 for the
formation of a poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole fibrous
material having an enhanced resistance to undergo color darkening
upon exposure to light wherein said
poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole is dissolved in said
spinning solution in a concentration of about 20 to 30 percent by
weight based upon the total weight of the solution.
15. An improved process in accordance with claim 12 for the
formation of a poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole fibrous
material having an enhanced resistance to undergo color darkening
upon exposure to light wherein said finely divided pigment is
arsenic thioarsenate.
16. An improved process in accordance with claim 12 for the
formation of a poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole fibrous
material having an enhanced resistance to undergo color darkening
upon exposure to light wherein said finely divided pigment is
copper phthalocyanine.
17. An improved process in accordance with claim 12 for the
formation of a poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole fibrous
material having an enhanced resistance to undergo color darkening
upon exposure to light wherein said finely divided pigment is
titanium dioxide.
18. An improved process in accordance with claim 12 for the
formation of a poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole fibrous
material having an enhanced resistance to undergo color darkening
upon exposure to light wherein said finely divided pigment is
substantially uniformly distributed within said
poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole fibrous material in a
concentration of about 0.2 to 3 percent by weight based upon the
weight of said poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole.
19. A polybenzimidazole fibrous material exhibiting an enhanced
resistance to undergo the usual darkening upon exposure to light
comprising about 0.1 to 8 percent by weight based upon the weight
of said polybenzimidazole of a finely divided pigment substantially
uniformly dispersed therein selected from the group consisting
essentially of arsenic thioarsenate, copper phthalocyanine, anatase
titanium dioxide, and mixtures of the foregoing.
20. A polybenzimidazole fibrous material in accordance with claim
19 exhibiting an enhanced resistance to undergo the usual darkening
upon exposure to light wherein said polybenzimidazole consists
essentially of recurring units of the formula: ##STR5##
21. A polybenzimidazole fibrous material in accordance with claim
20 exhibiting an enhanced resistance to undergo the usual darkening
upon exposure to light wherein said polybenzimidazole is
poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole.
22. A polybenzimidazole fibrous material in accordance with claim
21 exhibiting an enhanced resistance to undergo the usual darkening
upon exposure to light wherein said finely divided pigment is
substantially uniformly dispersed in said
poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole fibrous material in a
concentration of about 0.2 to 3 percent by weight based upon the
weight of said poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole.
23. A polybenzimidazole fibrous material in accordance with claim
22 exhibiting an enhanced resistance to undergo the usual darkening
upon exposure to light wherein said pigment is arsenic
thioarsenate.
24. A polybenzimidazole fibrous material in accordance with claim
22 exhibiting an enhanced resistance to undergo the usual darkening
upon exposure to light wherein said pigment is copper
phthalocyanine.
25. A polybenzimidazole fibrous material in accordance with claim
22 exhibiting an enhanced resistance to undergo the usual darkening
upon exposure to light wherein said pigment is anatase titanium
dioxide.
26. An improved solution suitable for the formation of shaped
polybenzimidazole articles comprising:
a. a solvent capable of dissolving the polybenzimidazole which is
selected from the group consisting essentially of
N,N-dimethylacetamide, N,N-dimethylformamide, dimethylsulfoxide,
and N-methyl-2-pyrrolidone,
b. dissolved polybenzimidazole, and
c. a minor concentration sufficient to stabilize the color of the
resulting shaped polybenzimidazole article of a finely divided
pigment which is dispersed in said solution selected from the group
consisting essentially of arsenic thioarsenate, copper
phthalocyanine, anatase titanium dioxide, and mixtures of the
foregoing.
27. An improved solution suitable for the formation of shaped
polybenzimidazole articles in accordance with claim 26 wherein said
polybenzimidazole consists essentially of recurring units of the
formula: ##STR6##
28. An improved solution suitable for the formation of shaped
polybenzimidazole articles in accordance with claim 27 wherein said
polybenzimidazole is
poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole.
29. An improved solution suitable for the formation of shaped
polybenzimidazole articles in accordance with claim 26 wherein said
solvent is N,N-dimethylacetamide.
30. An improved solution suitable for the formation of shaped
polybenzimidazole articles in accordance with claim 26 wherein said
finely divided pigment is arsenic thioarsenate.
31. An improved solution suitable for the formation of shaped
polybenzimidazole articles in accordance with claim 26 wherein said
finely divided pigment is copper phthalocyanine.
32. An improved solution suitable for the formation of shaped
polybenzimidazole articles in accordance with claim 26 wherein said
finely divided pigment is anatase titanium dioxide.
Description
BACKGROUND OF THE INVENTION
Polybenzimidazoles, and particularly aromatic polybenzimidazoles,
are characterized by a high degree of thermal stability. They may
be shaped to form fibers, films and other articles of wide utility
which show great resistance to degradation by heat, hydrolytic and
oxidizing media.
It has been found, however, that such shaped polybenzimidazole
articles darken rapidly, for example, in a few hours, from a
relatively light gold color to a dark, coffee or chocolate brown.
Although it is not understood, it is believed that the darkening is
due to some type of photodegradability of the polymer in which the
free amine end groups present in the polymer are affected. For
example, it has been postulated that hydrogen peroxide may be
formed from the polybenzimidazole polymer under certain conditions,
including the presence of air and moisture, which would tend to
react with the polymer chain. In addition, it has been suggested
that the repeating units of the polymer backbone may be oxidized to
a colored quinoid structure.
Regardless, however, the problem is known. A number of solutions
have been attempted to impart color stability to the
polybenzimidazole materials without success. For example,
commercial antioxidants and ultra-violet light absorbers have been
added to polybenzimidazole films and other articles. In addition, a
number of treatments to polybenzimidazole yarns, films and other
shaped articles such as scouring with nitrous acid and other
oxidizing or reducing materials, have been attempted. In addition,
a chrome treatment of the material has been attempted before
dyeing. While some of these treatments have been found to lighten
the ground color of the polybenzimidazole material, the material
still darkens upon exposure to light.
Commonly assigned U.S. Pat. No. 3,836,500 to Gordon W. Calundann
and George R. Ferment discloses that the color stability of
polybenzimidazole articles may be improved through the
incorporation of certain dissolved stabilizing reagents in a
solution of the polymer prior to article formation. Reagents there
utilized are: (1) an aliphatic carboxylic acid anhydride having 1
to about 6 carbon atoms, (2) aliphatic carboxylic acid halides
having 1 to about 6 carbon atoms, (3) tosyl chloride, and (4)
2,4-dinitrofluorobenzene.
Commonly assigned U.S. Ser. No. 536,807, filed Dec. 27, 1974 (now
U.S. Pat. No. 3,942,950), of Edward J. Powers and Walter P.
Hassinger, entitled "Improved Process for the Dyeing of
Polybenzimidazole Fibers with Anionic Dyestuffs" discloses a
technique whereby polybenzimidazole fibers may be successfully dyed
while accomplishing complete and uniform dye penetration. The
ability to produce satisfactorily dyed polybenzimidazole articles
which resist gradual darkening upon exposure to light over extended
periods of time is considered to be of prime importance if such
articles are to maintain the desired aesthetically pleasing shades
in combination with their other highly desirable utilitarian
characteristics.
It is an object of the present invention to provide a process
wherein the usual color darkening of a polybenzimidazole solid
material upon exposure to light is diminished.
It is an object of the present invention to provide a process
wherein the ground color inherently exhibited by polybenzimidazole
polymer may be stabilized and rendered more constant during
use.
It is an object of the present invention to improve the
lightfastness of solid polybenzimidazole polymer.
It is an object of the present invention to provide a
polybenzimidazole fibrous material exhibiting an enhanced
resistance to undergo the usual darkening upon exposure to
light.
It is another object of the present invention to provide a
polybenzimidazole fibrous material having improved color
stabilization without adversely influencing its desirable
non-burning characteristics.
It is a further object of the present invention to provide a
solution of a polybenzimidazole polymer which is capable of forming
polybenzimidazole shaped articles having an enhanced resistance to
darkening upon exposure to light.
These and other objects, as well as the scope, nature, and
utilization of the present invention will be apparent to those
skilled in the art from the following description and appended
claims.
SUMMARY OF THE INVENTION
It has been found that an improved solution suitable for the
formation of shaped polybenzimidazole articles comprises:
a. a solvent capable of dissolving the polybenzimidazole which is
selected from the group consisting essentially of
N,N-dimethylacetamide, N,N-dimethylformamide, dimethylsulfoxide,
and N-methyl-2-pyrrolidone,
b. dissolved polybenzimidazole, and
c. a minor concentration sufficient to stabilize the color of the
resulting shaped polybenzimidazole article of a finely divided
pigment which is dispersed in the solution selected from the group
consisting essentially of arsenic thioarsenate, copper
phthalocyanine, anatase titanium dioxide, and mixtures of the
foregoing.
It has been found that an improved process for the formation of a
polybenzimidazole solid material having an enhanced resistance to
undergo the usual color darkening upon exposure to light
comprises:
a. forming a solution of polybenzimidazole in a solvent selected
from the group consisting essentially of N,N-dimethylacetamide,
N,N-dimethylformamide, dimethylsulfoxide, and
N-methyl-2-pyrrolidone, with the solution having dispersed therein
a minor concentration of finely divided pigment selected from the
group consisting essentially of arsenic thioarsenate, copper
phthalocyanine, anatase titanium dioxide, and mixtures of the
foregoing, and
b. substantially removing said solvent from said polybenzimidazole
to form a polybenzimidazole solid material wherein said finely
divided pigment is substantially uniformly dispersed therein in a
concentration of about 0.1 to 8 percent by weight based upon the
weight of the polybenzimidazole.
It has been found that a polybenzimidazole fibrous material
exhibiting an enhanced resistance to undergo the usual darkening
upon exposure to light comprises about 0.1 to 8 percent by weight
based upon the weight of the polybenzimidazole of a finely divided
pigment substantially uniformly dispersed therein selected from the
group consisting essentially of arsenic thioarsenate, copper
phthalocyanine, anatase titanium dioxide, and mixtures of the
foregoing.
DESCRIPTION OF PREFERRED EMBODIMENTS
Polybenzimidazoles are a known class of heterocyclic polymers.
Typical polymers of this class are described in U.S. Pat. No.
2,895,948, U.S. Pat. No. Re. 26,065, and in the Journal of Polymer
Science, Vol. 50, pages 511-539 (1961) which are herein
incorporated by reference. The polybenzimidazoles consist
essentially of recurring units of the following Formulas I and II.
Formula I is: ##STR1## wherein R is a tetravalent aromatic nucleus,
preferably symmetrically substituted, with the nitrogen atoms
forming the benzimidazole rings being paired upon adjacent carbon
atoms, i.e. ortho carbon atoms of the aromatic nucleus, and R' is a
member of the class consisting of (1) an aromatic ring, (2) an
alkylene group (preferably those having 4 to 8 carbon atoms), and
(3) a heterocyclic ring from the class consisting of (a) pyridine,
(b) pyrazine, (c) furan, (d) quinoline, (e) thiophene, and (f)
pyran.
Formula II is: ##STR2## wherein Z is an aromatic nucleus having the
nitrogen atoms forming the benzimidazole ring paired upon adjacent
carbon atoms of the aromatic nucleus.
Preferably, aromatic polybenzimidazoles are selected, e.g. polymers
consisting essentially of the recurring units of Formulas I and II
wherein R' is at least one aromatic ring or a heterocyclic
ring.
As set forth in U.S. Pat. No. Re. 26,065, the aromatic
polybenzimidazoles having the recurring units of Formula II may be
prepared by self-condensing a trifunctional aromatic compound
containing only a single set of ortho disposed diamino substituents
and an aromatic, preferably phenyl, carboxylate ester substituent.
Exemplary of polymers of this type is poly-2,5(6)-benzimidazole
prepared by the autocondensation of phenyl-3,4-diaminobenzoate.
As also set forth in the above-mentioned patent, the aromatic
polybenzimidazoles having the recurring units of Formula I may be
prepared by condensing an aromatic tetraamine compound containing a
pair of orthodiamino substituents on the aromatic nucleus with a
dicarboxyl compound selected from the class consisting of (a) the
diphenyl ester of an aromatic dicarboxylic acid, (b) the diphenyl
ester of a heterocyclic dicarboxylic acid wherein the carboxyl
groups are substituents upon a carbon in a ring compound selected
from the class consisting of pyridine, pyrazine, furan, quinoline,
thiophene and pyran and (c) an anhydride of an aromatic
dicarboxylic acid.
Examples of polybenzimidazoles which have the recurring structure
of Formula I are as follows:
poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole;
poly-2,2'-(pyridylene 3",5")-5,5'-bibenzimidazole;
poly-2,2'-(furylene-2",5")-5,5'-bibenzimidazole;
poly-2,2'-(naphthalene-1",6")-5,5'-bibenzimidazole;
poly-2,2'-(biphenylene-4",4")-5,5'-bibenzimidazole;
poly-2,2'-amylene-5,5'-bibenzimidazole;
poly-2,2'-octamethylene-5,5'-bibenzimidazole;
poly-2,6-(m-phenylene)-dimidazobenzene;
poly-2,2'-cyclohexeneyl-5,5'-bibenzimidazole;
poly-2,2'-(m-phenylene)-5,5'-di(benzimidazole)ether;
poly-2,2'-(m-phenylene)-5,5'-di(benzimidazole)sulfide;
poly-2,2'-(m-phenylene)-5,5'-di(benzimidazole) sulfone;
poly-2,2'-(m-phenylene)-5,5'-di(benzimidazole) methane;
poly-2',2"-(m-phenylene)-5',5"-di(benzimidazole) propane-2,2;
and
poly-2',2"-(m-phenylene)-5',5"-di(benzimidazole) ethylene-1,2
where the double bonds of the ethylene groups are intact in the
final polymer.
The preferred polybenzimidazole for use in the present process is
poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole, the recurring unit of
which is: ##STR3##
Any polymerization process known to those skilled in the art may be
employed to prepare the polybenzimidazole which may then be formed
into a fibrous material. Representative techniques for preparing
the polybenzimidazole are disclosed in U.S. Pat. Nos. 3,509,108;
3,549,603; and 3,551,389, which are assigned to the assignee of the
present invention and are herein incorporated by reference.
With respect to aromatic polybenzimidazoles, preferably equimolar
quantities of the monomeric tetraamine and dicarboxyl compound are
introduced into a first stage melt polymerization reaction zone and
heated therein at a temperature above about 200.degree. C.,
preferably at least 250.degree. C., and more preferably from about
270.degree. to 300.degree. C. The reaction is conducted in a
substantially oxygen-free atmosphere, i.e., below about 20 ppm
oxygen and preferably below about 8 ppm oxygen, until a foamed
prepolymer is formed having an inherent viscosity, expressed as
deciliters per gram, of at least 0.1 and preferably from about 0.13
to 0.3, the inherent viscosity (I.V.) as used herein being
determined from a solution of 0.4 grams of the polymer in 100 ml.
of 97 percent H.sub.2 SO.sub.4 at 25.degree. C.
After the conclusion of the first stage reaction, which normally
takes at least 0.5 hour and preferably 1 to 3 hours, the foamed
prepolymer is cooled and then powdered or pulverized in any
convenient manner. The resulting prepolymer powder is then
introduced into a second stage polymerization reaction zone wherein
it is heated under substantially oxygen-free conditions, as
described above, to yield a polybenzimidazole polymer product,
desirably having an I.V., as measured above, of at least 0.6, e.g.
0.80 to 1.1 or more.
The temperature employed in the second stage is at least
250.degree. C., preferably at least 325.degree. C., and more
preferably from about 350.degree. to 425.degree. C. The second
stage reaction generally takes at least 0.5 hour, and preferably
from about 1 to 4 hours or more.
A particularly preferred method for preparing the polybenzimidazole
is disclosed in the aforesaid U.S. Pat. No. 3,509,108. As disclosed
therein aromatic polybenzimidazoles may be prepared by initially
reacting the monomer in a melt phase polymerization at a
temperature above about 200.degree. C. and a pressure above 50 psi
(e.g., 300 to 600 psi) and then heating the resulting reaction
product in a solid state polymerization at a temperature above
about 300.degree. C. (e.g., 350.degree. to 500.degree. C.) to yield
the final product.
The polybenzimidazole is dissolved in an appropriate solvent and a
minor concentration of the finely divided pigment (described
hereafter) is dispersed therein. The solvents suitable for use in
the present invention are N,N-dimethylacetamide,
N,N-dimethylformamide, dimethylsulfoxide, and
N-methyl-2-pyrrolidone. The particularly preferred solvent is
N,N-dimethylacetamide. The concentration of the polybenzimidazole
in the solution may be varied widely. For instance, when forming a
solution suitable for extrusion through a shaped orifice to form a
fibrous material, the polybenzimidazole may be dissolved in the
solvent to yield a final solution containing the polymer in a
concentration of about 10 to 45 percent by weight based upon the
total weight of the solution, preferably from about 20 to 30
percent by weight. When the solution is to be used for the casting
of a film, the polybenzimidazole may be dissolved in the solvent in
a concentration of about 5 to 30 percent by weight based upon the
total weight of the solution, preferably from about 15 to 25
percent by weight. When the solution is to be used for the ultimate
precipitation of a molding compound, the polybenzimidazole may be
dissolved in the solvent in a concentration of about 5 to 35
percent by weight based upon the total weight of the solution,
preferably from about 15 to 25 percent by weight.
One suitable means for dissolving the polymer in the solvent is by
mixing the materials at a temperature above the atmospheric boiling
point of the solvent, for example 25.degree. to 120.degree. C.
above such boiling point, and at a pressure of 2 to 15 atmospheres
for a period of 1 to 5 hours.
The finely divided pigments (described hereafter) may be dispersed
in the solution of polybenzimidazole polymer by introduction into
the previously formed solution with stirring. A preferred procedure
for introducing the pigment is to add a concentrated suspension of
the pigment in the same solvent to the polymer solution in a
pressure vessel and to tumble the mixture at an elevated
temperature until good mixing is accomplished. The concentrated
suspension of the pigment initially may be formed by ball milling
with the solvent. Alternatively, the dry pigment may be ball milled
directly into the solution of polybenzimidazole polymer. The
pigment is introduced in a minor concentration sufficient to
stabilize the color of the resulting polybenzimidazole solid which
is formed upon the subsequent removal of the solvent (described
hereafter). For instance, the finely divided pigment may be
provided in the solution in a concentration of about 0.1 to 8
percent by weight based upon the weight of the dissolved
polybenzimidazole, and preferably in a concentration of about 0.2
to 3 percent by weight.
The finely divided pigments are insoluble in the solvent and
commonly possess a number average particle size up to about 5
microns, e.g. about 0.05 to 5 microns, and preferably about 0.1 to
2 microns. When the solution containing dissolved polybenzimidazole
polymer is ultimately to be used for fiber formation, care must be
taken to insure that the dispersed pigment is not of sufficient
particle size to obstruct the orifice of the spinning machine.
The finely divided pigments utilized in the present process have
surprisingly been found capable of enhancing the resistance of a
polybenzimidazole solid material to undergo the usual color
darkening upon exposure to light and may be arsenic thioarsenate,
copper phthalocyanine, anatase titanium dioxide, or mixtures of the
same.
The arsenic thioarsenate pigment is free-flowing yellow powder and
possesses the structural formula As(AsS.sub.4). While arsenic
thioarsenate is a recognized antioxidant, it was found that other
well known antioxidants are unsuitable for use in the present
invention and fail to impart the desired color stability to a
polybenzimidazole. It has been found that the presence of the
yellow arsenic thioarsenate within the light brown
polybenzimidazole polymer results in practically no color change.
Also, the usual darkening upon exposure to light is greatly
retarded. Particularly satisfactory results are achieved when a
minor concentration (e.g. 0.3 percent by weight based upon the
weight of the polybenzimidazole) of a UV light absorber is used in
combination with the arsenic thioarsenate. A preferred UV light
absorber is a benzylidene malonic ester available from the American
Cyanamid Corporation under the designation Cyasorb UV1988
absorber.
The copper phthalocyanine pigment is preferably of the beta-type
which tends to be more stable than the alpha-type. The copper
phthalocyanine has the ability to color the polybenzimidazole to a
green shade which resists darkening upon exposure to light and
thereby protects the polybenzimidazole.
The anatase titanium dioxide pigment is sometimes identified as
octahedrite and serves to lighten and deluster the color of the
polybenzimidazole. It has been found however that the presence of
the anatase titanium dioxide pigment surprisingly serves an
additional role of providing stabilization with respect to the
usual color darkening upon exposure to light. Other inorganic
pigments, such as rutile titanium dioxide, and zinc sulfide lack
this highly desirable stabilization property when incorporated in a
polybenzimidazole.
As previously indicated, other additives such as antioxidants and
UV light absorbers optionally may be utilized in combination with
the above-identified pigments.
The solvent is removed from the solution of polybenzimidazole to
form a polybenzimidazole solid material wherein the finely divided
pigment is substantially uniformly dispersed therein in a
concentration of about 0.1 to 8 percent by weight based upon the
weight of the polybenzimidazole (preferably in a concentration of
about 0.2 to 3 percent by weight). For instance, the solvent may be
removed via a conventional dry spinning technique by extrusion
through a shaped orifice into an evaporative atmosphere to form a
fibrous material. The solvent may be removed by a conventional
casting technique wherein the solvent is evaporated from a thin
layer of solution to form a film. Alternatively, the solvent may be
removed by contact with agitation with a solvent-miscible
non-solvent for the polybenzimidazole (e.g. ketones such as acetone
and methylethyl ketone, alcohols such as methanol and ethanol,
aromatics such as benzene and toluene, chlorinated aliphatics such
as chloroform and methylene chloride, and water) and the resulting
polybenzimidazole recovered as a particulate solid which is
suitable for use as a molding compound which may be sintered to
form a three-dimensional shaped article. In all instances, the
pigment is substantially uniformly dispersed in the resulting
polybenzimidazole solid material and the product exhibits an
enhanced resistance to undergo the usual color darkening upon
exposure to light.
In a particularly preferred embodiment of the invention the
polybenzimidazole solution containing dispersed pigment is dry spun
to form a fibrous material. For example, the solutions may be
extruded through a spinneret into a conventional type downdraft
spinning column containing a circulating inert gas such as
nitrogen, noble gases, combustion gases, or superheated stem.
Conveniently, the spinneret face is at a temperature of from about
100.degree. to 170.degree. C., the top of the column from about
120.degree. to 220.degree. C., the middle of the column from about
140.degree. to 250.degree. C., and the bottom of the column from
about 160.degree. to 320.degree. C. After leaving the spinning
column, the continuous filamentary materials are taken up, for
example, at a speed within the range of about 50 to 350 meters or
more per minute. If the continuous filamentary materials are to be
washed while wound on bobbins, the resulting "as-spun" materials
may be subjected to a slight steam drawing treatment at a draw
ratio of from about 1.05:1 to 1.5:1 in order to prevent the fibers
from relaxing and falling off the bobbin during the subsequent
washing step. Further details with respect to a method for
dry-spinning a continuous length of a polybenzimidazole fibrous
material are shown in U.S. Pat. No. 3,502,756 to Bohrer et al.
which is assigned to the same assignee as the present invention and
is herein incorporated by reference.
The continuous length of polybenzimidazole fibrous material next
may be washed so as to remove at least the major portion of
residual spinning solvent, e.g., so that the washed materials
contain less than about 1 percent by weight solvent based on the
weight of the continuous filamentary material, and preferably so as
to obtain an essentially spinning solvent-free fibrous material
(i.e. a fibrous material containing less than about 0.1 percent
solvent by weight). Typically, a simple water wash is employed;
however, if desired, other wash material such as acetone, methanol,
methylethyl ketone and similar solvent-miscible and volatile
organic solvents may be used in place of or in combination with the
water. The washing operation may be conducted by collecting the
polybenzimidazole fibrous material on perforated rolls or bobbins,
immersing the rolls in the liquid wash bath and pressure washing
the fibrous material, for example, for about 2 to 48 hours or more.
Alternatively, the continuous length of polybenzimidazole fibrous
material may be washed on a continuous basis by passing the fibrous
material in the direction of its length through one or more liquid
wash baths (e.g. for 1 to 10 minutes). Any wash technique known to
those skilled in the art may be selected. The occluded pigment is
not removed by the washing.
The continuous length of polybenzimidazole fibrous material may
next be dried to remove the liquid wash bath by any convenient
technique. For instance, the drying operation for bobbins of yarn
may be conducted at a temperature of about 150.degree. to
300.degree. C. for about 2 to 100 hours or more. Alternatively, the
continuous length of polybenzimidazole fibrous material may be
dried on a continuous basis by passing the fibrous material in the
direction of its length through an appropriate drying zone (e.g. an
oven provided at 300.degree. to 400.degree. C. for 1 to 2 minutes).
If drying is employed, preferably the drying temperature does not
exceed about 250.degree. C. for several hours or 400.degree. C. for
more than 1 minute, as above these limits degradation of the fiber
may occur.
The polybenzimidazole fibrous material preferably next may be hot
drawn at a draw ratio of about 2:1 to 5:1 in order to enhance its
orientation. Representative draw procedures are disclosed in
commonly assigned U.S. Pat. Nos. 3,622,660, and 3,849,529.
The polybenzimidazole fibrous material when intended for textile
applications is usually crimped and cut into stable form. For
example a crimp of about 10 to 15 crimps per inch may be imparted
to the same prior to cutting into lengths of about 2 inches. This
crimped staple fiber may then be spun into yarns of from about 14's
to 60's cotton count. Fabric nest may be formed by weaving or
knitting.
The theory whereby the arsenic thioarsenate, copper phthalocyanine,
and anatase titanium dioxide pigments are capable of enhancing the
resistance of the polybenzimidazole to undergo the usual color
darkening upon exposure to light is considered to be complex and
incapable of simple explanation.
The following examples are given as specific illustrations of the
invention. It should be understood, however, that the invention is
not limited to the specific details set forth in the examples.
EXAMPLE I
Poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole is prepared in
accordance with Example I of U.S. Pat. No. 3,509,108 and is
dissolved in N,N-dimethylacetamide in a concentration of 23 percent
by weight based upon the total weight of the solution. 0.5 percent
by weight of finely divided arsenic thioarsenate pigment based upon
the weight of the poly-2,2'-(m-phenylene)-5,5-bibenzimidazole is
dispersed within the solution via ball milling. The arsenic
thioarsenate is available from the El Monte Chemical Co. under the
designation of Arsenone S arsenic thioarsenate, and possesses a
number average particle size of about one micron.
The resulting solution containing the dispersed pigment has a
viscosity of about 1000 poise at 30.degree. C., and is dry spun by
extrusion through a shaped orifice to form a fibrous material and
is subsequently hot drawn in accordance with conventional
techniques. Arsenic thioarsenate pigment is substantially uniformly
dispersed in the resulting fibrous material in a concentration of
about 0.5 percent by weight based upon the weight of the
polybenzimidazole. The resulting fibrous material is colorstable
and maintains its color without any significant darkening for over
10 standard fading hours in a Carbon Arc Fade-Ometer.
Fibrous materials which lack the arsenic thioarsenate pigment
darken very rapidly upon exposure to sunlight.
EXAMPLE II
Example I is repeated with the exception that 0.2 percent by weight
arsenic thioarsenate and 0.3 percent by weight benzylidene malonic
ester UV absorber (i.e. Cyasorb UV 1988 absorber available from the
American Cyanamid Corporation) are uniformly dispersed in the
resulting fibrous material. The color stability of the product is
found to be even greater.
EXAMPLE III
Example I is repeated with the exception that beat-copper
phthalocyanine pigment is substituted for the arsenic thioarsenate
pigment. The pigment colors the fibrous material to an attractive
green color. The pigment is available from the Chemetron
Corporation under the designation of Phthalo Blue G beta-copper
phthalocyanine pigment, and possesses a number average particle
size of about one micron.
Substantially similar results are achieved with respect to
resistance to darkening upon exposure to light.
EXAMPLE IV
Example I is repeated with the exception that anatase titanium
dioxide pigment is substituted for the arsenic thioarsenate
pigment. The pigment is available from the American Cyanamid
Corporation under the designation of Calcotone White anatase
titanium dioxide pigment, and possesses a number average particle
size of about 0.2 micron. The pigment serves to lighten and to
deluster the resulting fibrous material.
Substantially similar results are achieved with respect to
resistance to darkening upon exposure to light.
EXAMPLE V
Arsenic thioarsenate pigment, arsenic thioarsenate pigment in
combination with UV absorber, beta-copper phthalocyanine pigment,
and anatase titanium dioxide pigment are charged to four separate
solutions of poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole in
N,N-dimethylacetamide. The polymer is dissolved in the solutions in
a concentration of 23 percent by weight based upon the total weight
of the solution, and 0.2, 0.2, 3, and 1 percent by weight
respectively of each pigment is dispersed therein based upon the
weight of the poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole. A
control solution (without any pigment) also is prepared. Films are
formed from each solution by casting the solutions upon a glass
support and drying at 100.degree. C. under reduced pressure with a
slight air flow over the film. After drying the films are readily
stripped from the support. Color shade changes in the films after
10 SFH (Standard Fading Hours) in a Carbon Arc Fade-Ometer are
reported below. The results illustrate the enhanced resistance of
the films formed in accordance with the present invention to
undergo the usual color darkening upon exposure to light.
______________________________________ Film Color.sup.1 as after
Pigment cast 10SFH Contrast.sup.2
______________________________________ None (control) 1 6 P Arsenic
thioarsenate 1 2 G Arsenic thioarsenate plus Cyasorb UV 1988 (0.3%)
1 1 E Beta-copper phthalocyanine Green Green E Anatase titanium
dioxide <1 2 G ______________________________________ .sup.1
Color is rated by comparison to a set of polymethylmethacrylate
standards number 1 to 6 containing 1.0% to 2.0% amber dye
respectively, i 0.2% increments. .sup.2 Adjective rating (E is
excellent, G is good, F is fair and P is poor) as described in
Federal Test Method Standard No. 191, Method 5660.0 Section
5.7.2.
COMPARATIVE EXAMPLE
Various known inorganic additives, antioxidants, ultra-violet light
absorbers and mixtures are added in various amounts (by weight of
the polymer) to a 15% solution of the polybenzimidazole of Example
I in N,N-dimethylacetamide. Films are cast and Film Color is
determined before and after 10 SFH in the Carbon Arc Fade-Ometer in
the same manner as Example IV. The additives, amounts and results
are shown below.
______________________________________ Film Color As After Additive
(amount) cast 10 SFH ______________________________________ None
(Control) 1 >6 Rutile titanium dioxide 1 >6 Zinc sulfide 1
>6 Santowhite.sup.1 (5.0%) 2 4 Cyasorb UV1988.sup.2 (5.0%) 1 4
Santowhite (0.4%) plus Cyasorb UV1988 (0.6%) 1 3 Santowhite (2.0%)
plus Cyasorb UV1988 (3.0%) 1 6 Irganox 1076.sup.3 (5.0%) 4 3
Irganox 1076 (0.4%) plus Cyasorb UV1988 (0.6%) 1 3 Irganox 1076
(2.0%) plus Cyasorb UV1988 (3.0%) 4 5 Irganox 1010.sup.4 (5.0%) 1 4
Cyasorb UV207.sup.5 (5.0%) 2 4 Irganox 1010 (0.3%) plus Cyasorb
UV207 (0.6%) 1 3 Irganox 1010 (2.0%) plus Cyasorb UV207 (3.0%) 3 5
______________________________________ .sup.1 Santowhite is an
alkylidene bisphenol antioxidant available from the Monsanto
Company. .sup.2 Cyasorb UV1988 is a benzylidene malonic ester
ultra-violet absorbe available from the American Cyanamid Company.
.sup.3 Irganox 1076 is an alkyl phenol antioxidant available from
the Geigy-Ciba Chemical Company .sup.4 Irganox 1010 is an
alkylidene bisphenol antioxidant availabe from the Geigy-Ciba
Chemical Company. .sup.5 Cyasorb UV207 is a hydroxybenzophenone
ultra-violet absorber available from the American Cyanamid
Company.
Although the invention has been described with preferred
embodiments, it is to be understood that variations and
modifications may be resorted to as will be apparent to those
skilled in the art. Such variations and modifications are to be
considered within the purview and the scope of the claims appended
hereto.
* * * * *